The present invention relates to plain bearings and in particular but not exclusively to main bearings and thrust bearings.
Combined plain journal bearings and thrust bearings in the form of flanges and being of unitary construction are well known. They are, however, expensive to produce owing to the very tight tolerances required in their manufacture. In flanged main bearing form very fine tolerances are also required on the housing into which the bearing is to fit. The dimension between the inner opposing faces of the thrust bearings must be held to particularly close tolerances since if too much axial flexure of the thrust bearing occurs fatigue may result with possibly disastrous results.
Generally, such bearings are formed from a single piece of flat strip by appropriate machinery. Attempts have been made to make bearings by a more economical route by, for example, welding the thrust bearing to the journal bearing end faces. Whilst this route may be somewhat cheaper, the same limitation as to tolerances still applies.
Because of the above problems, engine manufacturers have wherever possible tried to use conventional plain journal bearings and separate thrust washers. Running tolerance on crankshaft end float is easily maintained in this case by controlling the wall thickness of the thrust washer.
In recent years engine manufacturers have been placing increased emphasis on the use of robotics in engine assembly. Whilst many assembly operations are amenable to robotics, the installation of separate journal bearings and thrust washers is particularly troublesome. The thrust washers are prone to drop out of the housing before the crankshaft is fitted or they can be fitted back to front. Some of these problems may not come to light until serious damage to the engine has occurred.
In UKP No. 1,297,559 Hill et al describes a flanged half-bearing wherein the flanges are produced separately from the half-bearing but which are attached thereto by means of co-operating slots and lugs. However, even this method of retaining the flanges is not altogether suitable for robotic assembly since the flanges are easily dislodged from the journal bearing during handling.
Evidently the solution to the robotics problem is to have the journal bearing and thrust bearing as a single unit instead of in separate pieces. However, with conventional flanged bearings the expense problem still remains.